Aminomethylene complexes of divalent tungsten and molybdenum

Article abstract of DOI:10.1021/om9707073

Convenient routes are reported to aminomethylene complexes of divalent molybdenum and tungsten: [M(=CHNⁱPr₂)(CO)₂(S₂CA)₂] (M = Mo, W; A = NMe₂, NEt₂, N(CH₂)₄, OEt).

Full text of DOI:10.1021/om9707073

5616
Organometallics 1997, 16, 5616-5617
Am in om eth ylen e Com p lexes of Diva len t Tu n gsten a n d
Molybd en u m
Darren J . Cook and Anthony F. Hill*
Department of Chemistry, Imperial College of Science, Technology, and Medicine,
South Kensington, London SW7 2AY, U.K.
Received August 11, 1997X
Summary: Convenient routes are reported to aminom-
ethylene complexes of divalent molybdenum and tung-
sten: [M(dCHNiPr2)(CO)2(S2CA)2] (M ) Mo, W; A )
NMe2, NEt2, N(CH2)4, OEt).
of [M(CO)6] with LiNiPr2, Cl2PPh3, and PPh3 (Scheme
2). These complexes react with [Et2NH2][S2CNEt2],
[NH4][S2CN(CH2)4], or hydrated Na[S2CNMe2] to pro-
vide the neutral red aminomethylene complexes
[M(dCHNiPr2)(CO)2(S2CNR2)2] (M ) W, NR2 ) NMe2
(2a ), NEt2 (2b), N(CH2)4 (2c); M ) Mo, NR2 ) N(CH2)4
(2d )) in high yields.9 Alternatively, the same complexes
result in moderate yields in a direct “one-pot” synthesis
from the successive treatment of [M(CO)6] with LiNi-
Pr2, (CF3CO)2O, and the appropriate dithiocarbamate
salt. It is noteworthy that both approaches fail for
chromium, providing only [Cr(S2CNR2)3], while all-
trans-[W(tCNiPr2)(O2CCF3)(CO)2(PPh3)2] fails to react
with a variety of dithiocarbamate salts. Xanthate-
coordinated analogues, e.g., [W(dCHNiPr2)(CO)2(S2-
COEt)2] (2e), are however accessible in a similar man-
ner directly from [W(CO)6] (or from preformed (1a )) if
K[S2COEt] is employed in addition to NH4Cl (as a
proton source). The tungsten complexes are compara-
tively robust; however, the molybdenum complexes are
decomposed rapidly by air to provide [Mo(dO)2(S2-
CNR2)2].
Aminomethylene complexes of the group 6 metals are
confined to zerovalent metal centers or divalent metals
coligated by cyclopentadienyl or poly(pyrazolyl)borate
ligands.1 Early indications that amino substituents
could stabilize carbene ligands bound to mid-valent
group 6 metal centers were provided by the observations
of Kreissl: while [W(tCC6H4Me-4)(CO)2(η-C5H5)] reacts
with hydrogen chloride to provide the acyl complex
[W(η2-OCCH2C6H4Me-4)Cl2(CO)(η-C5H5)],2 the same re-
agent with [W(tCNEt2)(CO)2(η-C5H5)] provides the
aminomethylene complex [W(dCHNEt2)Cl(CO)2(η-
C5H5)].3 Similar results have been recently obtained by
Filippou for chromium.4 Continuing our studies on the
reactivity of aminomethylidyne complexes of groups 65
and 8,6 we have now investigated the reactions of the
complexes [M(tCNiPr2)Cl(CO)3L] (M ) Mo, W; L ) CO,
PPh3)5 with dithiocarbamate and xanthate salts. Herein,
we wish to report that these reactions provide conve-
nient access to a range of stable aminomethylene
complexes of divalent molybdenum and tungsten.
The reactions of alkylidyne complexes of tungsten
with dithiocarbamates have already been shown by
Mayr to be complex, providing either ketenyl7 or thio-
aldehyde8 complexes, depending on the nature of the
carbamate countercation (Scheme 1). For the latter
outcome, [R2NH2][S2CNR2] is employed as the dithio-
carbamate source and it is reasonable to postulate
benzylidene intermediates resulting from the protona-
tion of an anionic alkylidyne complex, although such
intermediates have yet to be observed in this case. The
complexes [M(tCNiPr2)Cl(CO)3(PPh3)] (M ) Mo (1a ),
W (1b)) are conveniently obtained5b from the reactions
The formulation of the complexes 2 rests on elemental
microanalytical, spectroscopic, and FAB-MS data.9 While
FAB-MS data confirm the gross formulation, the most
informative spectroscopic data are associated with the
aminomethylene ligand: 13C{1H} resonances are ob-
served in the region 233.1-249.5 ppm for each of the
complexes and for the pyrollidynyl dithioate examples
2c and 2d proton-coupled spectra revealed J (CH) to be
139.2 and 141.0 Hz, respectively. The 1H NMR data
for the complexes 2 include singlet resonances in the
i
low-field region of δ 11.85-12.35 ppm. The Pr reso-
nances (two heptets and two doublets) confirm that the
(9) Selected data for new complexes are as follows: (25 °C; IR, ν-
(CO), CH2Cl2; NMR, CDCl3; satisfactory microanalytical data obtained).
2a : [W(CO)6] (4.3 mmol) in diethyl ether (30 mL) was treated with
LDA (4.3 mmol) and cooled (0 °C). Ph3PCl2 (4.3 mmol) was added, and
the suspension was stirred for 5 min. Na[S2CNMe2]‚2H2O (9.0 mmol)
was then added, and after stirring for 1 h, the supernatant was
chromatographed (alumina, 10 °C, Et2O). Addition of ethanol and
concentration of the eluate resulted in deep orange-red microcrystals.
Yield: 1.42 g (51%). IR: 1914, 1817 cm-1. NMR: 1H, δ 1.19, 1.33 [d ×
2, 12 H, CHCH3], 3.25 [s, 12 H, NCH3], 3.84, 4.44 [h × 2, 2 H, CHCH3],
11.95 [s, 1 H, WdCHN]; 13C{1H} δ 248.7 [WCO, J (WC) 132 Hz], 236.4
[WdCH, J (WC) 84 Hz], 209.2 [S2CNMe2], 60.8, 51.2 [CHCH3], 39.2
[NCH3], 23.9, 21.1 [CHCH3]. FAB-MS: m/z 594 [M]+, 565 [M - CO]+,
537 [M - 2CO]+. 3: yield 44% directly from [W(CO)6]. IR: 1987, 1897
cm-1. NMR: 1H, δ 2.29 [s, 6 H, CCH3], 2.84, 2.92 [s × 2, 6 H, NCH3],
6.83 [d, 2 H, H3,5(C6H3)], 7.04 [t, 1 H, H4(C6H3)]; 13C{1H}, 284.1 [WtC,
J (PC) 10 Hz], 226.8 [2 C, CO, J (PC) 5 Hz], 213.6 [CO, J (PC) 52 Hz],
207.7 [S2C], 139.9-126.8 [C6H3 and C6H5], 39.7, 39.4 [NCH3], 20.9
[CCH3]. FAB-MS: m/z 739 [M]+, 711 [M - CO]+, 682 [M - 2CO]+,
420 [M - PPh3 - 2CO]+. 4a : yield 39% directly from [W(CO)6]. IR:
1922 cm-1. NMR: 1H, δ 3.30, 3.32, 3.34, 3.72 [s × 4, 12 H, NCH3],
3.79 [s, 3 H, OCH3], 5.50 [s, 1 H, CHS], 6.82, 7.07 [d × 2, 4 H, C6H4];
13C{1H}, δ 259.2 [NCS], 217.9 [CO], 215.9 [NCS2], 159.0 [SCH], 139.7-
113.0 [C6H4], 56.7, 55.3, 40.7, 39.6 [NCH3], 48.2 [OCH3]. FAB-MS: m/z
574 [M]+, 544 [M - CO]+.
* To whom correspondence should be addressed. E-mail:
a.hill@ic.ac.uk.
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) For a recent review of alkylidene complexes of the group 6 metals
see: Winter, M. In Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
U.K., 1996; Vol. 5.
(2) Kreissl, F. R.; Sieber, W. J .; Wolfgruber, M.; Riede, J . Angew.
Chem., Int. Ed. Engl. 1984, 23, 640. Kreissl, F. R.; Sieber, W. J .; Keller,
H.; Riede, J .; Wolfgruber, M. J . J . Organomet. Chem. 1987, 320, 83.
(3) Kreissl, F. R.; Sieber, W. J .; Wolfgruber, M. J . Organomet. Chem.
1984, 270, C45.
(4) Filippou, A. C.; Wossner, D.; Lungwitz, B.; Kociokkohn, G.
Angew. Chem., Int. Ed. Engl. 1996, 35, 876.
(5) (a) Anderson, A.; Hill, A. F. J . Organomet. Chem. 1990, 394, C24.
(b) Anderson, S.; Cook, D. J .; Hill, A. F. J . Organomet. Chem. 1993,
463, C3.
(6) Anderson, S.; Hill, A. F. Organometallics, 1995, 14, 1562.
(7) For a review of dithiocarbamate-induced ketenyl formation see:
Mayr, A.; Bastos, C. M. Prog. Inorg. Chem. 1992, 40, 1.
(8) (a) Mayr, A.; McDermott, G. A.; Dorries, A. M.; Holder, A. K.;
Fultz, W. C.; Rheingold, A. L. J . Am. Chem. Soc. 1986, 108, 310. (b)
Anderson, S.; Hill, A. F. J . Chem. Soc., Dalton Trans. 1993, 587.
S0276-7333(97)00707-3 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 26, 1997 5617
Sch em e 1. Keten yl vs Th ioa ld eh yd e F or m a tion a ,8a
a
Reagents: (i) Na[S2CNEt2]‚2H2O; (ii) [Et2NH2][S2CNEt2].
Sch em e 2a
alkylidyne complex [W(tCC6H3Me2-2,6)(S2CNMe2)(CO)2-
(PPh3)] (3) or the thioaldehyde complexes [W(η2-
SCHAr)(CO)(η2-SCNEt2)(S2CNEt2)] (R ) C6H4OMe-4
(4b), 2-C4H3S (4c), 1-C10H7 (4d )) are obtained, which
are analogous to the previously reported complexes
[W(η2-SCHAr)(CO)(η2-SCNEt2)(S2CNEt2)] (Ar ) Ph
(4a ),8a C5H4Mn(CO)3 (4e)8b). In direct reactions begin-
ning with [W(CO)6] the same thioaldehyde complexes
are obtained. The alkylidyne complex 3 is obtained by
sequential treatment of [W(CO)6] with LiC6H3Me2-2,6,
(CF3CO)2O, PPh3, and Na[S2CNMe2]. Thus, it has not
been possible to isolate either benzylidene or ketenyl
complexes from these reactions and it appears that the
unique electronic properties of the amino substituent
are crucial for the stabilization of the aminomethylene
complexes 2. Similarly, the dithiocarbamate-induced
progress from alkylidyne to alkylidene to thioaldehyde
appears to be intercepted at the dithiocarbamato-
alkylidyne stage by inclusion of sterically cumbersome
substituents in the case of 3.
Aminomethylene complexes of zerovalent group 6
metals have increasingly attracted attention for use in
organic synthesis.10 The reactivity of the alkylidene
ligand may, in principle, be modified by the nature of
the metal center (oxidation state, coordinative satura-
tion, d configuration, and chirality). The convenient and
large-scale access to aminomethylene complexes of
divalent group 6 metals offered by the present strategies
makes the complexes 2 intriguing candidates for further
reactivity studies, which we are currently pursuing.
a
Reagents: (i) Na[S2CNMe2]‚2H2O, R ) C6H3Me2-2,6; (ii)
[Et2NH2][S2CNEt2], R ) C6H4OMe-2, C4H3S-2, C10H7-1; (iii)
LiR, LiBr, (CF3CO)2O, PPh3, R ) C6H3Me2-2,6, C6H4OMe-2,
C4H3S-2, C10H7-1; (iv) LiNiPr2, Cl2PPh3, Na[S2CNMe2]‚2H2O
(X ) NMe2); (v) LiNiPr2, Cl2PPh3, PPh3; (vi) M ) Mo, W,
Na[S2CNMe2]‚2H2O, NH4[S2CN(CH2)4], [Et2NH2][S2CNEt2], or
NH4Cl + K[S2COEt].
Ack n ow led gm en t. We wish to thank the Engineer-
ing and Physical Sciences Research Council (U.K.).
A.F.H. gratefully acknowledges the award of a Senior
Research Fellowship by the Royal Society and the
Leverhulme Trust.
NiPr2 group is no longer coordinated to a linear sp-
hybridized carbon. These data are all consistent with
the presence of the aminomethylene ligand. Signals due
1
to the carbamate substituents in both the 13C and H
NMR spectra indicate a fluxional time averaging of their
chemical environments in the seven-coordinate com-
plexes.
Su p p or tin g In for m a tion Ava ila ble: Synthetic details,
spectroscopic data, and elemental analyses for all new com-
pounds (9 pages). Ordering information is given on any
current masthead page.
Given the remarkable stability of the aminomethylene
complexes, the reactivity of the related arylmethylidyne
complexes [M(tCAr)Br(CO)3(PPh3)] (M ) Mo, W; Ar )
C6H3Me2-2,6, C6H4OMe-4, C10H7-1) and all-trans-
[M(tCC4H3S-2)Br(CO)2(PPh3)2] toward dithiocarbamate
salts was also investigated. For the molybdenum
complexes, the only isolable products were [Mo(dO)2-
(S2CNR2)2]. For the tungsten examples, however, the
OM9707073
(10) For
a discussion of aminomethylene complexes in organic
synthesis, see: Wulff, W. D. In Comprehensive Organometallic Chem-
istry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: Oxford, U.K., 1996; Vol. 12.